The present invention relates to an image display for displaying a half-tone image such as a television image through the utilization of a double-isolated thin-film display panel.
A prior art technique to obtain a half-tone image is to employ an analog-to-digital converter which provides a predetermined number of tone signals indicative of each of the sliced levels of video signals. This results in unnecessary complexity in circuit construction.
It is therefore an object of the present invention to provide a means for displaying a half-tone image such as a television image without using a analog-to-digital converter. To obtain a half-tone display, the present invention employs a thin-film EL display panel and practices amplitude modulation wherein the amplitude of a pulse voltage applied to the thin-film EL display panel is varied in accordance with video signals. In one preferred form thereof, a constant current amount or an enabling period of a constant current element provided within a discharge circuit is varied according to video signals, thereby controlling the pre-charge amplitude on the thin-film EL panel. The amount of the discharge of the pre-charge on the EL panel is controlled by the video signals.
As a result, the brightness of the EL display panel corresponds to video signals.
According to a television receiver embodying the present invention, video signals are stored for respective ones of the horizontal scanning electrodes during a single horizontal scanning slot of a television signal and the thin-film EL panel is charged in advance. In the presence of a horizontal synchronizing signal, the amplitude of the pre-charge on the thin-film EL panel is controlled by the thus stored video signals within a constant current discharge circuit constituted by a constant current element. A write voltage is applied to the thin-film EL panel during the first half of the next succeeding horizontal scanning slot and the pre-charge operation described above is carried out during the second half of that horizontal scanning slot.